Insulin Receptors in Isolated Adult Mouse Intestinal Cells: Studiesin Vivoand in Organ Culture*

Abstract

Isolated intestinal cells from adult mice possess a high concentration of insulin receptors. The binding capacity and the number of binding sites are higher in duodenum than in jejunum or ileum and in the upper part of the villus than in the crypts. The specific binding is, respectively, 11.8 .+-. 1.0%, 9.1 .+-. 4.0% and 5.5 .+-. 0.3%/mg .cntdot. protein for duodenum, jejunum and ileum. The number of high affinity sites per cell is, respectively, 11.0 .times. 103, 3 .times. 103 and 2.5 .times. 103. The number of low affinity sites per cell is, respectively, 11.0 .times. 104, 4.1 .times. 103 and 3.9 .times. 103. This specific binding increases to 15.9 + 0.9% after 24 h of fasting and to 24.5 .+-. 2.2% mg protein after 48 h of fasting. This increase is due not only to an increment in the number of sites but also to alterations in affinity constants (K1, control, 0.380, 48-h fasting, 0.044 .times. 109 M-1; K2, control, 1.20, 48-h fasting; 2.61 .times. 107 M-1). The receptors are mainly located on the basolateral and internal membranes (P1, 9.4 .+-. 0.7%/mg protein), but are also present on brush border membranes (P2, 2.6 .+-. 1.1%/mg protein, P < 0.01). After 24 h of organ culture, the specific binding is not modified in duodenal explants. Moreover, in the presence of insulin in the culture medium, the binding is decreased by 59%.